The Debian package management system, when used properly, offers the user to install consistent sets of binary packages to the system from the archive. Currently, there are 44893 packages available for the amd64 architecture.

The Debian package management system has a rich history and many choices for the front end user program and back end archive access method to be used. Currently, we recommend the following.

apt-get(8) for all commandline operations, including package installation and removal, and dist-upgrades.

aptitude(8) for an interactive text interface to manage the installed packages and to search the available packages.

2.1. Debian package management prerequisites

2.1.1. Package configuration

Here are some key points for package configuration on the Debian system.

The manual configuration by the system administrator is respected. In other words, the package configuration system makes no intrusive configuration for the sake of convenience.

Each package comes with its own configuration script with standardized user interface called debconf(7) to help initial installation process of the package.

Debian Developers try their best to make your upgrade experience flawless with package configuration scripts.

Full functionalities of packaged software are available to the system administrator. But ones with security risks are disabled in the default installation.

If you manually activate a service with some security risks, you are responsible for the risk containment.

Esoteric configuration may be manually enabled by the system administrator. This may create interferences with popular generic helper programs for the system configuration.

2.1.2. Basic precautions

Warning

Do not install packages from random mixture of suites. It probably breaks the package consistency which requires deep system management knowledge, such as compiler ABI, library version, interpreter features, etc.

The newbie Debian system administrator should stay with the stable release of Debian while applying only security updates. I mean that some of the following valid actions are better avoided, as a precaution, until you understand the Debian system very well. Here are some reminders.

Do not include testing or unstable in "/etc/apt/sources.list".

Do not mix standard Debian with other non-Debian archives such as Ubuntu in "/etc/apt/sources.list".

Do not create "/etc/apt/preferences".

Do not change default behavior of package management tools through configuration files without knowing their full impacts.

Do not overwrite system files by installing software programs directly compiled from source.

Install them into "/usr/local" or "/opt", if needed.

The non-compatible effects caused by above actions to the Debian package management system may leave your system unusable.

The serious Debian system administrator who runs mission critical servers, should use extra precautions.

Do not install any packages including security updates from Debian without thoroughly testing them with your particular configuration under safe conditions.

You as the system administrator are responsible for your system in the end.

The long stability history of the Debian system is no guarantee by itself.

2.1.3. Life with eternal upgrades

Despite my warnings above, I know many readers of this document wish to run the testing or unstable suites of Debian as their main system for self-administered Desktop environments. This is because they work very well, are updated frequently, and offer the latest features.

Caution

For your production server, the stable suite with the security updates is recommended. The same can be said for desktop PCs on which you can spend limited administration efforts, e.g. for your mother's PC.

It takes no more than simply setting the distribution string in the "/etc/apt/sources.list" to the suite name: "testing" or "unstable"; or the codename: "stretch" or "sid". This makes you live the life of eternal upgrades.

The use of testing or unstable is a lot of fun but comes with some risks. Even though the unstable suite of the Debian system looks very stable for most of the times, there have been some package problems on the testing and unstable suite of the Debian system and a few of them were not so trivial to resolve. It may be quite painful for you. Sometimes, you may have a broken package or missing functionality for a few weeks.

Here are some ideas to ensure quick and easy recovery from bugs in Debian packages.

Make the system dual bootable by installing the stable suite of the Debian system to another partition

Here, I tend to use codename "jessie" instead of suite name "stable" to avoid surprises when the next stable is released.

The meaning of "/etc/apt/sources.list" is described in sources.list(5) and key points are followings.

The "deb" line defines for the binary packages.

The "deb-src" line defines for the source packages.

The 1st argument is the root URL of the Debian archive.

The 2nd argument is the distribution name: either the suite name or the codename.

The 3rd and following arguments are the list of valid archive area names of the Debian archive.

The "deb-src" lines can safely be omitted (or commented out by placing "#" at the start of the line) if it is just for aptitude which does not access source related meta data. It speeds up the updates of the archive meta data. The URL can be "http://", "ftp://", "file://", ….

Tip

If "sid" is used in the above example instead of "jessie", the "deb: http://security.debian.org/ …" line for security updates in the "/etc/apt/sources.list" is not required. This is because there is no security update archive for "sid" (unstable).

Here is the list of URL of the Debian archive sites and suite name or codename used in the configuration file.

Only pure stable release with security updates provides the best stability. Running mostly stable release mixed with some packages from testing or unstable release is riskier than running pure unstable release for library version mismatch etc. If you really need the latest version of some programs under stable release, please use packages from jessie-updates and http://backports.debian.org (see Section 2.7.4, “Updates and Backports”) services. These services must be used with extra care.

Caution

You should basically list only one of stable, testing, or unstable suites in the "deb" line. If you list any combination of stable, testing, and unstable suites in the "deb" line, APT programs slow down while only the latest archive is effective. Multiple listing makes sense for these when the "/etc/apt/preferences" file is used with clear objectives (see Section 2.7.3, “Tweaking candidate version”).

Tip

For the Debian system with the stable and testing suites, it is a good idea to include lines with "http://security.debian.org/" in the "/etc/apt/sources.list" to enable security updates as in the example above.

Note

The security bugs for the stable archive are fixed by the Debian security team. This activity has been quite rigorous and reliable. Those for the testing archive may be fixed by the Debian testing security team. For severalreasons, this activity is not as rigorous as that for stable and you may need to wait for the migration of fixed unstable packages. Those for the unstable archive are fixed by the individual maintainer. Actively maintained unstable packages are usually in a fairly good shape by leveraging latest upstream security fixes. See Debian security FAQ for how Debian handles security bugs.

The Debian archive organization can be studied best by pointing your browser to the each archive URL appended with dists or pool.

The distribution is referred by two ways, the suite or codename. The word distribution is alternatively used as the synonym to the suite in many documentations. The relationship between the suite and the codename can be summarized as the following.

In the stricter Debian archive terminology, the word "section" is specifically used for the categorization of packages by the application area. (Although, the word "main section" may sometimes be used to describe the Debian archive area named as "main".)

Every time a new upload is done by a Debian developer (DD) to the unstable archive (via incoming processing), the DD is required to ensure uploaded packages to be compatible with the latest set of packages in the latest unstable archive.

If DD breaks this compatibility intentionally for important library upgrade etc, there is usually announcement to the debian-devel mailing list etc.

Before a set of packages are moved by the Debian archive maintenance script from the unstable archive to the testing archive, the archive maintenance script not only checks the maturity (about 10 days old) and the status of the RC bug reports for the packages but also tries to ensure them to be compatible with the latest set of packages in the testing archive. This process makes the testing archive very current and usable.

Through the gradual archive freeze process led by the release team, the testing archive is matured to make it completely consistent and bug free with some manual interventions. Then the new stable release is created by assigning the codename for the old testing archive to the new stable archive and creating the new codename for the new testing archive. The initial contents of the new testing archive is exactly the same as that of the newly released stable archive.

Both the unstable and the testing archives may suffer temporary glitches due to several factors.

Broken package upload to the archive (mostly for unstable)

Delay of accepting the new packages to the archive (mostly for unstable)

Archive synchronization timing issue (both for testing and unstable)

Manual intervention to the archive such as package removal (more for testing) etc.

So if you ever decide to use these archives, you should be able to fix or work around these kinds of glitches.

Caution

For about few months after a new stable release, most desktop users should use the stable archive with its security updates even if they usually use unstable or testing archives. For this transition period, both unstable and testing archives are not good for most people. Your system is difficult to keep in good working condition with the unstable archive since it suffers surges of major upgrades for core packages. The testing archive is not useful either since it contains mostly the same content as the stable archive without its security support (Debian testing-security-announce 2008-12). After a month or so, the unstable archive may be usable if you are careful.

Tip

When tracking the testing archive, a problem caused by a removed package is usually worked around by installing corresponding package from the unstable archive which is uploaded for bug fix.

We will be guided by the needs of our users and the free software community. We will place their interests first in our priorities. We will support the needs of our users for operation in many different kinds of computing environments. We will not object to non-free works that are intended to be used on Debian systems, or attempt to charge a fee to people who create or use such works. We will allow others to create distributions containing both the Debian system and other works, without any fee from us. In furtherance of these goals, we will provide an integrated system of high-quality materials with no legal restrictions that would prevent such uses of the system.

Works that do not meet our free software standards

We acknowledge that some of our users require the use of works that do not conform to the Debian Free Software Guidelines. We have created "contrib" and "non-free" areas in our archive for these works. The packages in these areas are not part of the Debian system, although they have been configured for use with Debian. We encourage CD manufacturers to read the licenses of the packages in these areas and determine if they can distribute the packages on their CDs. Thus, although non-free works are not a part of Debian, we support their use and provide infrastructure for non-free packages (such as our bug tracking system and mailing lists).

Users should be aware of the risks of using packages in the non-free and contrib areas:

lack of freedom for such software packages

lack of support from Debian on such software packages (Debian can't support software properly without having access to its source code.)

contamination of your 100% free Debian system

The Debian Free Software Guidelines are the free software standards for Debian. Debian interprets "software" in the widest scope including document, firmware, logo, and artwork data in the package. This makes Debian's free software standards very strict ones.

In order to meet this strict free software standards required for main, Debian unbrands Mozilla software packages such as Firefox, Thunderbird, and Seamonkey by removing their logo and some artwork data; and ships them as Iceweasel, Icedove, and Iceape, respectively.

Typical non-free and contrib packages include freely distributable packages of following types:

Document packages under GNU Free Documentation License with invariant sections such as ones for GCC and Make. (mostly found in the non-free/doc section.)

Game and font packages with restriction on commercial use and/or content modification.

Please note that the number of non-free and contrib packages is less than 2% of that of main packages. Enabling access to the non-free and contrib areas does not obscure the source of packages. Interactive full screen use of aptitude(8) provides you with full visibility and control over what packages are installed from which area to keep your system as free as you wish.

2.1.6. Package dependencies

The Debian system offers a consistent set of binary packages through its versioned binary dependency declaration mechanism in the control file fields. Here is a bit over simplified definition for them.

"Depends"

This declares an absolute dependency and all of the packages listed in this field must be installed at the same time or in advance.

"Pre-Depends"

This is like Depends, except that it requires completed installation of the listed packages in advance.

"Recommends"

This declares a strong, but not absolute, dependency. Most users would not want the package unless all of the packages listed in this field are installed.

"Suggests"

This declares a weak dependency. Many users of this package may benefit from installing packages listed in this field but can have reasonable functions without them.

"Enhances"

This declares a week dependency like Suggests but works in the opposite direction.

"Breaks"

This declares a package incompatibility usually with some version specification. Generally the resolution is to upgrade all of the packages listed in this field.

"Conflicts"

This declares an absolute incompatibility. All of the packages listed in this field must be removed to install this package.

"Replaces"

This is declared when files installed by this package replace files in the listed packages.

"Provides"

This is declared when this package provide all of the files and functionality in the listed packages.

Note

Please note that defining "Provides", "Conflicts" and "Replaces" simultaneously to an virtual package is the sane configuration. This ensures that only one real package providing this virtual package can be installed at any one time.

Fetch selected binary packages from remote archive if candidate version is different from installed version

Unpack fetched binary packages

Run preinst script

Install binary files

Run postinst script

Install ("aptitude install …" or "apt-get install …"):

Chose packages listed on the command line

Make package dependency resolution

Fetch selected binary packages from remote archive

Unpack fetched binary packages

Run preinst script

Install binary files

Run postinst script

Remove ("aptitude remove …" or "apt-get remove …"):

Chose packages listed on the command line

Make package dependency resolution

Run prerm script

Remove installed files except configuration files

Run postrm script

Purge ("aptitude purge …" or "apt-get purge …"):

Chose packages listed on the command line

Make package dependency resolution

Run prerm script

Remove installed files including configuration files

Run postrm script

Here, I intentionally skipped technical details for the sake of big picture.

2.1.8. First response to package management troubles

You should read the fine official documentation. The first document to read is the Debian specific "/usr/share/doc/<package_name>/README.Debian". Other documentation in "/usr/share/doc/<package_name>/" should be consulted too. If you set shell as Section 1.4.2, “Customizing bash”, type the following.

$ cd <package_name>
$ pager README.Debian
$ mc

You may need to install the corresponding documentation package named with "-doc" suffix for detailed information.

2.2. Basic package management operations

Repository based package management operations on the Debian system can be performed by many APT-based package management tools available on the Debian system. Here, we explain 2 basic package management tools: apt-get / apt-cache and aptitude.

For the package management operation which involves package installation or updates package metadata, you need to have root privilege.

2.2.1. apt-get / apt-cache vs. aptitude

Although aptitude is a very nice interactive tool which the author mainly uses, you should know some cautionary facts:

The aptitude command is not recommended for the release-to-release system upgrade on the stable Debian system after the new release.

The use of "apt-get dist-upgrade" is recommended for it. See Bug #411280.

The aptitude command sometimes suggests mass package removals for the system upgrade on the testing or unstable Debian system.

This situation has frightened many system administrators. Don't panic.

This seems to be caused mostly by the version skew among packages depended or recommended by a meta-package such as gnome-core.

This can be resolved by selecting "Cancel pending actions" in the aptitude command menu, exiting aptitude, and using "apt-get dist-upgrade".

The apt-get and apt-cache commands are the most basic APT-based package management tools.

apt-get and apt-cache offer only the commandline user interface.

apt-get is most suitable for the major system upgrade between releases, etc.

apt-get offers a robust package dependency resolver.

apt-get is less demanding on hardware resources. It consumes less memory and runs faster.

apt-cache offers a standard regex based search on the package name and description.

apt-get and apt-cache can manage multiple versions of packages using /etc/apt/preferences but it is quite cumbersome.

The aptitude command is the most versatile APT-based package management tool.

aptitude offers the fullscreen interactive text user interface.

aptitude offers the commandline user interface, too.

aptitude is most suitable for the daily interactive package management such as inspecting installed packages and searching available packages.

aptitude is more demanding on hardware resources. It consumes more memory and runs slower.

aptitude offers an enhanced regex based search on all of the package metadata.

aptitude can manage multiple versions of packages without using /etc/apt/preferences and it is quite intuitive.

2.2.2. Basic package management operations with the commandline

Here are basic package management operations with the commandline using aptitude(8) and apt-get(8) /apt-cache(8).

install candidate version of installed packages without removing any other packages

aptitude full-upgrade

apt-get dist-upgrade

install candidate version of installed packages while removing other packages if needed

aptitude remove foo

apt-get remove foo

remove "foo" package while leaving its configuration files

N/A

apt-get autoremove

remove auto-installed packages which are no longer required

aptitude purge foo

apt-get purge foo

purge "foo" package with its configuration files

aptitude clean

apt-get clean

clear out the local repository of retrieved package files completely

aptitude autoclean

apt-get autoclean

clear out the local repository of retrieved package files for outdated packages

aptitude show foo

apt-cache show foo

display detailed information about "foo" package

aptitude search <regex>

apt-cache search <regex>

search packages which match <regex>

aptitude why <regex>

N/A

explain the reason why <regex> matching packages should be installed

aptitude why-not <regex>

N/A

explain the reason why <regex> matching packages can not be installed

Note

Although the aptitude command comes with rich features such as its enhanced package resolver, this complexity has caused (or may still causes) some regressions such as Bug #411123, Bug #514930, and Bug #570377. In case of doubt, please use the apt-get and apt-cache commands over the aptitude command.

The "aptitude why <regex>" can list more information by "aptitude -v why <regex>". Similar information can be obtained by "apt-cache rdepends <package>".

When aptitude command is started in the commandline mode and faces some issues such as package conflicts, you can switch to the full screen interactive mode by pressing "e"-key later at the prompt.

You may provide command options right after "aptitude".

Table 2.7. Notable command options for aptitude(8)

command option

description

-s

simulate the result of the command

-d

download only but no install/upgrade

-D

show brief explanations before the automatic installations and removals

See aptitude(8) and "aptitude user's manual" at "/usr/share/doc/aptitude/README" for more.

Tip

The dselect package is still available and was the preferred full screen interactive package management tool in previous releases.

2.2.3. Interactive use of aptitude

For the interactive package management, you start aptitude in interactive mode from the console shell prompt as follows.

$ sudo aptitude -u
Password:

This updates the local copy of the archive information and display the package list in the full screen with menu. Aptitude places its configuration at "~/.aptitude/config".

Tip

If you want to use root's configuration instead of user's one, use "sudo -H aptitude …" instead of "sudo aptitude …" in the above expression.

Tip

Aptitude automatically sets pending actions as it is started interactively. If you do not like it, you can reset it from menu: "Action" → "Cancel pending actions".

2.2.4. Key bindings of aptitude

Notable key strokes to browse status of packages and to set "planned action" on them in this full screen mode are the following.

Table 2.8. List of key bindings for aptitude

key

key binding

F10 or Ctrl-t

menu

?

display help for keystroke (more complete listing)

F10 → Help → User's Manual

display User's Manual

u

update package archive information

+

mark the package for the upgrade or the install

-

mark the package for the remove (keep configuration files)

_

mark the package for the purge (remove configuration files)

=

place the package on hold

U

mark all upgradable packages (function as full-upgrade)

g

start downloading and installing selected packages

q

quit current screen and save changes

x

quit current screen and discard changes

Enter

view information about a package

C

view a package's changelog

l

change the limit for the displayed packages

/

search for the first match

\

repeat the last search

The file name specification of the command line and the menu prompt after pressing "l" and "//" take the aptitude regex as described below. Aptitude regex can explicitly match a package name using a string started by "~n and followed by the package name.

Tip

You need to press "U" to get all the installed packages upgraded to the candidate version in the visual interface. Otherwise only the selected packages and certain packages with versioned dependency to them are upgraded to the candidate version.

2.2.5. Package views under aptitude

In the interactive full screen mode of aptitude(8), packages in the package list are displayed as the next example.

idA libsmbclient -2220kB 3.0.25a-1 3.0.25a-2

Here, this line means from the left as the following.

The "current state" flag (the first letter)

The "planned action" flag (the second letter)

The "automatic" flag (the third letter)

The Package name

The change in disk space usage attributed to "planned action"

The current version of the package

The candidate version of the package

Tip

The full list of flags are given at the bottom of Help screen shown by pressing "?".

When <regex_pattern> is a null string, place "~T" immediately after the command.

Here are some short cuts.

"~P<term>" == "~Dprovides:<term>"

"~C<term>" == "~Dconflicts:<term>"

"…~W term" == "(…|term)"

Users familiar with mutt pick up quickly, as mutt was the inspiration for the expression syntax. See "SEARCHING, LIMITING, AND EXPRESSIONS" in the "User's Manual" "/usr/share/doc/aptitude/README".

Note

With the lenny version of aptitude(8), the new long form syntax such as "?broken" may be used for regex matching in place for its old short form equivalent "~b". Now space character "" is considered as one of the regex terminating character in addition to tilde character "~". See "User's Manual" for the new long form syntax.

2.2.8. Dependency resolution of aptitude

The selection of a package in aptitude not only pulls in packages which are defined in its "Depends:" list but also defined in the "Recommends:" list if the menu "F10 → Options → Preferences → Dependency handling" is set accordingly. These auto installed packages are removed automatically if they are no longer needed under aptitude.

2.3.2. Browsing with the regex matching

The regex "~dipv6" in the "New Flat Package List" view with "l" prompt, limits view to packages with the matching description and let you browse their information interactively.

2.3.3. Purging removed packages for good

You can purge all remaining configuration files of removed packages.

Check results of the following command.

# aptitude search '~c'

If you think listed packages are OK to be purged, execute the following command.

# aptitude purge '~c'

You may want to do the similar in the interactive mode for fine grained control.

You provide the regex "~c" in the "New Package View" view with "l" prompt. This limits the package view only to regex matched packages, i.e., "removed but not purged". All these regex matched packages can be shown by pressing "[" at top level headings.

Then you press "_" at top level headings such as "Not Installed Packages". Only regex matched packages under the heading are marked to be purged by this. You can exclude some packages to be purged by pressing "=" interactively for each of them.

This technique is quite handy and works for many other command keys.

2.3.4. Tidying auto/manual install status

Here is how I tidy auto/manual install status for packages (after using non-aptitude package installer etc.).

The "m" action over "Tasks" is an optional one to prevent mass package removal situation in future.

2.3.5. System wide upgrade

Note

When moving to a new release etc, you should consider to perform a clean installation of new system even though Debian is upgradable as described below. This provides you a chance to remove garbages collected and exposes you to the best combination of latest packages. Of course, you should make a full backup of system to a safe place (see Section 10.2, “Backup and recovery”) before doing this. I recommend to make a dual boot configuration using different partition to have the smoothest transition.

You can perform system wide upgrade to a newer release by changing contents of the "/etc/apt/sources.list" file pointing to a new release and running the "apt-get update; apt-get dist-upgrade" command.

In reality, you may face some complications due to some package transition issues, mostly due to package dependencies. The larger the difference of the upgrade, the more likely you face larger troubles. For the transition from the old stable to the new stable after its release, you can read its new Release Notes and follow the exact procedure described in it to minimize troubles.

When you decide to move from stable to testing before its formal release, there are no Release Notes to help you. The difference between stable and testing could have grown quite large after the previous stable release and makes upgrade situation complicated.

You should make precautionary moves for the full upgrade while gathering latest information from mailing list and using common senses.

2.4. Advanced package management operations

2.4.1. Advanced package management operations with commandline

Here are list of other package management operations for which aptitude is too high-level or lacks required functionalities.

Table 2.13. List of advanced package management operations

command

action

COLUMNS=120 dpkg -l <package_name_pattern>

list status of an installed package for the bug report

dpkg -L <package_name>

list contents of an installed package

dpkg -L <package_name> | egrep '/usr/share/man/man.*/.+'

list manpages for an installed package

dpkg -S <file_name_pattern>

list installed packages which have matching file name

apt-file search <file_name_pattern>

list packages in archive which have matching file name

apt-file list <package_name_pattern>

list contents of matching packages in archive

dpkg-reconfigure <package_name>

reconfigure the exact package

dpkg-reconfigure -p=low <package_name>

reconfigure the exact package with the most detailed question

configure-debian

reconfigure packages from the full screen menu

dpkg --audit

audit system for partially installed packages

dpkg --configure -a

configure all partially installed packages

apt-cache policy <binary_package_name>

show available version, priority, and archive information of a binary package

apt-cache madison <package_name>

show available version, archive information of a package

apt-cache showsrc <binary_package_name>

show source package information of a binary package

apt-get build-dep <package_name>

install required packages to build package

aptitude build-dep <package_name>

install required packages to build package

apt-get source <package_name>

download a source (from standard archive)

dget <URL for dsc file>

download a source packages (from other archive)

dpkg-source -x <package_name>_<version>-<debian_version>.dsc

build a source tree from a set of source packages ("*.orig.tar.gz" and "*.debian.tar.gz"/"*.diff.gz")

debuild binary

build package(s) from a local source tree

make-kpkg kernel_image

build a kernel package from a kernel source tree

make-kpkg --initrd kernel_image

build a kernel package from a kernel source tree with initramfs enabled

dpkg -i <package_name>_<version>-<debian_version>_<arch>.deb

install a local package to the system

debi <package_name>_<version>-<debian_version>_<arch>.dsc

install local package(s) to the system

dpkg --get-selections '*' >selection.txt

save dpkg level package selection state information

dpkg --set-selections <selection.txt

set dpkg level package selection state information

echo <package_name> hold | dpkg --set-selections

set dpkg level package selection state for a package to hold (equivalent to "aptitude hold <package_name>")

Note

For a package with the multi-arch feature, you may need to specify the architecture name for some commands. For example, use "dpkg -L libglib2.0-0:amd64" to list contents of the libglib2.0-0 package for the amd64 architecture.

Caution

Lower level package tools such as "dpkg -i …" and "debi …" should be carefully used by the system administrator. It does not automatically take care required package dependencies. Dpkg's commandline options "--force-all" and similar (see dpkg(1)) are intended to be used by experts only. Using them without fully understanding their effects may break your whole system.

Please note the following.

All system configuration and installation commands require to be run from root.

2.4.2. Verification of installed package files

The installation of debsums enables verification of installed package files against MD5sum values in the "/var/lib/dpkg/info/*.md5sums" file with debsums(1). See Section 10.3.5, “The MD5 sum” for how MD5sum works.

Note

Because MD5sum database may be tampered by the intruder, debsums(1) is of limited use as a security tool. It is only good for checking local modifications by the administrator or damage due to media errors.

2.4.3. Safeguarding for package problems

Many users prefer to follow the unstable release of the Debian system for its new features and packages. This makes the system more prone to be hit by the critical package bugs.

The installation of the apt-listbugs package safeguards your system against critical bugs by checking Debian BTS automatically for critical bugs when upgrading with APT system.

The installation of the apt-listchanges package provides important news in "NEWS.Debian" when upgrading with APT system.

2.4.4. Searching on the package meta data

Although visiting Debian site http://packages.debian.org/ facilitates easy ways to search on the package meta data these days, let's look into more traditional ways.

The grep-dctrl(1), grep-status(1), and grep-available(1) commands can be used to search any file which has the general format of a Debian package control file.

The "dpkg -S <file_name_pattern>" can be used search package names which contain files with the matching name installed by dpkg. But this overlooks files created by the maintainer scripts.

If you need to make more elaborate search on the dpkg meta data, you need to run "grep -e regex_pattern *" command in the "/var/lib/dpkg/info/" directory. This makes you search words mentioned in package scripts and installation query texts.

If you wish to look up package dependency recursively, you should use apt-rdepends(8).

2.5. Debian package management internals

Let's learn how the Debian package management system works internally. This should help you to create your own solution to some package problems.

2.5.1. Archive meta data

Meta data files for each distribution are stored under "dist/<codename>" on each Debian mirror sites, e.g., "http://ftp.us.debian.org/debian/". Its archive structure can be browsed by the web browser. There are 6 types of key meta data.

Table 2.14. The content of the Debian archive meta data

file

location

content

Release

top of distribution

archive description and integrity information

Release.gpg

top of distribution

signature file for the "Release" file signed with the archive key

Contents-<architecture>

top of distribution

list of all files for all the packages in the pertinent archive

Release

top of each distribution/area/architecture combination

archive description used for the rule of apt_preferences(5)

Packages

top of each distribution/area/binary-architecture combination

concatenated debian/control for binary packages

Sources

top of each distribution/area/source combination

concatenated debian/control for source packages

In the recent archive, these meta data are stored as the compressed and differential files to reduce network traffic.

2.5.2. Top level "Release" file and authenticity

Tip

The top level "Release" file is used for signing the archive under the secure APT system.

Each suite of the Debian archive has a top level "Release" file, e.g., "http://ftp.us.debian.org/debian/dists/unstable/Release", as follows.

Here, you can find my rationale to use the "suite", and "codename" in Section 2.1.4, “Debian archive basics”. The "distribution" is used when referring to both "suite" and "codename". All archive "area" names offered by the archive are listed under "Components".

The integrity of the top level "Release" file is verified by cryptographic infrastructure called the secure apt.

The cryptographic signature file "Release.gpg" is created from the authentic top level "Release" file and the secret Debian archive key.

The public Debian archive key can be seeded into "/etc/apt/trusted.gpg";

automatically by installing the keyring with the latest base-files package, or

The secure APT system verifies the integrity of the downloaded top level "Release" file cryptographically by this "Release.gpg" file and the public Debian archive key in "/etc/apt/trusted.gpg".

The integrity of all the "Packages" and "Sources" files are verified by using MD5sum values in its top level "Release" file. The integrity of all package files are verified by using MD5sum values in the "Packages" and "Sources" files. See debsums(1) and Section 2.4.2, “Verification of installed package files”.

2.5.3. Archive level "Release" files

Tip

The archive level "Release" files are used for the rule of apt_preferences(5).

There are archive level "Release" files for all archive locations specified by "deb" line in "/etc/apt/sources.list", such as "http://ftp.us.debian.org/debian/dists/unstable/main/binary-amd64/Release" or "http://ftp.us.debian.org/debian/dists/sid/main/binary-amd64/Release" as follows.

For "Archive:" stanza, suite names ("stable", "testing", "unstable", …) are used in the Debian archive while codenames ("dapper", "feisty", "gutsy", "hardy", "intrepid", …) are used in the Ubuntu archive.

For some archives, such as experimental, and jessie-backports, which contain packages which should not be installed automatically, there is an extra line, e.g., "http://ftp.us.debian.org/debian/dists/experimental/main/binary-amd64/Release" as follows.

Please note that for normal archives without "NotAutomatic: yes", the default Pin-Priority value is 500, while for special archives with "NotAutomatic: yes", the default Pin-Priority value is 1 (see apt_preferences(5) and Section 2.7.3, “Tweaking candidate version”).

2.5.4. Fetching of the meta data for the package

When APT tools, such as aptitude, apt-get, synaptic, apt-file, auto-apt, … are used, we need to update the local copies of the meta data containing the Debian archive information. These local copies have following file names corresponding to the specified distribution, area, and architecture names in the "/etc/apt/sources.list" (see Section 2.1.4, “Debian archive basics”).

First 4 types of files are shared by all the pertinent APT commands and updated from command line by "apt-get update" or "aptitude update". The "Packages" meta data are updated if there is the "deb" line in "/etc/apt/sources.list". The "Sources" meta data are updated if there is the "deb-src" line in "/etc/apt/sources.list".

The "Packages" and "Sources" meta data contain "Filename:" stanza pointing to the file location of the binary and source packages. Currently, these packages are located under the "pool/" directory tree for the improved transition over the releases.

Local copies of "Packages" meta data can be interactively searched with the help of aptitude. The specialized search command grep-dctrl(1) can search local copies of "Packages" and "Sources" meta data.

Local copy of "Contents-<architecture>" meta data can be updated by "apt-file update" and its location is different from other 4 ones. See apt-file(1). (The auto-apt uses different location for local copy of "Contents-<architecture>.gz" as default.)

2.5.5. The package state for APT

In addition to the remotely fetched meta data, the APT tool after lenny stores its locally generated installation state information in the "/var/lib/apt/extended_states" which is used by all APT tools to track all auto installed packages.

2.5.6. The package state for aptitude

In addition to the remotely fetched meta data, the aptitude command stores its locally generated installation state information in the "/var/lib/aptitude/pkgstates" which is used only by it.

2.5.7. Local copies of the fetched packages

All the remotely fetched packages via APT mechanism are stored in the "/var/cache/apt/archives" until they are cleaned.

This cache file cleaning policy for aptitude can be set under "Options" → "Preferences" and it may be forced by its menu "Clean package cache" or "Clean obsolete files" under "Actions".

The debian-installer (d-i) uses udeb as the file extension for its binary package instead of normal deb. An udeb package is a stripped down deb package which removes few non-essential contents such as documentation to save space while relaxing the package policy requirements. Both deb and udeb packages share the same package structure. The "u" stands for micro.

2.5.9. The dpkg command

dpkg(1) is the lowest level tool for the Debian package management. This is very powerful and needs to be used with care.

While installing package called "<package_name>", dpkg process it in the following order.

the stat override information used by dpkg(1) and set by dpkg-statoverride(8)

/var/lib/dpkg/status

the status information for all the packages

/var/lib/dpkg/status-old

the first-generation backup of the "var/lib/dpkg/status" file

/var/backups/dpkg.status*

the second-generation backup and older ones of the "var/lib/dpkg/status" file

The "status" file is also used by the tools such as dpkg(1), "dselect update" and "apt-get -u dselect-upgrade".

The specialized search command grep-dctrl(1) can search the local copies of "status" and "available" meta data.

Tip

In the debian-installer environment, the udpkg command is used to open udeb packages. The udpkg command is a stripped down version of the dpkg command.

2.5.10. The update-alternatives command

The Debian system has mechanism to install somewhat overlapping programs peacefully using update-alternatives(8). For example, you can make the vi command select to run vim while installing both vim and nvi packages.

The Debian alternatives system keeps its selection as symlinks in "/etc/alternatives/". The selection process uses corresponding file in "/var/lib/dpkg/alternatives/".

2.5.11. The dpkg-statoverride command

Stat overrides provided by the dpkg-statoverride(8) command are a way to tell dpkg(1) to use a different owner or mode for a file when a package is installed. If "--update" is specified and file exists, it is immediately set to the new owner and mode.

Caution

The direct alteration of owner or mode for a file owned by the package using chmod or chown commands by the system administrator is reset by the next upgrade of the package.

Note

I use the word file here, but in reality this can be any filesystem object that dpkg handles, including directories, devices, etc.

2.5.12. The dpkg-divert command

File diversions provided by the dpkg-divert(8) command are a way of forcing dpkg(1) not to install a file into its default location, but to a diverted location. The use of dpkg-divert is meant for the package maintenance scripts. Its casual use by the system administrator is deprecated.

2.6. Recovery from a broken system

When running unstable system, the administrator is expected to recover from broken package management situation.

Caution

Some methods described here are high risk actions. You have been warned!

2.6.1. Incompatibility with old user configuration

If a desktop GUI program experienced instability after significant upstream version upgrade, you should suspect interferences with old local configuration files created by it. If it is stable under a newly created user account, this hypothesis is confirmed. (This is a bug of packaging and usually avoided by the packager.)

To recover stability, you should move corresponding local configuration files and restart the GUI program. You may need to read old configuration file contents to recover configuration information later. (Do not erase them too quickly.)

2.6.2. Different packages with overlapped files

Archive level package management systems, such as aptitude(8) or apt-get(1), do not even try to install packages with overlapped files using package dependencies (see Section 2.1.6, “Package dependencies”).

Errors by the package maintainer or deployment of inconsistently mixed source of archives (see Section 2.7.2, “Packages from mixed source of archives”) by the system administrator may create a situation with incorrectly defined package dependencies. When you install a package with overlapped files using aptitude(8) or apt-get(1) under such a situation, dpkg(1) which unpacks package ensures to return error to the calling program without overwriting existing files.

Caution

The use of third party packages introduces significant system risks via maintainer scripts which are run with root privilege and can do anything to your system. The dpkg(1) command only protects against overwriting by the unpacking.

You can work around such broken installation by removing the old offending package, <old-package>, first.

$ sudo dpkg -P <old-package>

2.6.3. Fixing broken package script

When a command in the package script returns error for some reason and the script exits with error, the package management system aborts their action and ends up with partially installed packages. When a package contains bugs in its removal scripts, the package may become impossible to remove and quite nasty.

For the package script problem of "<package_name>", you should look into following package scripts.

"/var/lib/dpkg/info/<package_name>.preinst"

"/var/lib/dpkg/info/<package_name>.postinst"

"/var/lib/dpkg/info/<package_name>.prerm"

"/var/lib/dpkg/info/<package_name>.postrm"

Edit the offending package script from the root using following techniques.

disable the offending line by preceding "#"

force to return success by appending the offending line with "|| true"

Configure all partially installed packages with the following command.

# dpkg --configure -a

2.6.4. Rescue with the dpkg command

Since dpkg is very low level package tool, it can function under the very bad situation such as unbootable system without network connection. Let's assume foo package was broken and needs to be replaced.

You may still find cached copies of older bug free version of foo package in the package cache directory: "/var/cache/apt/archives/". (If not, you can download it from archive of http://snapshot.debian.net/ or copy it from package cache of a functioning machine.)

If you can boot the system, you may install it by the following command.

If your system is unbootable from hard disk, you should seek other ways to boot it.

Boot the system using the debian-installer CD in rescue mode.

Mount the unbootable system on the hard disk to "/target".

Install older version of foo package by the following.

# dpkg --root /target -i /path/to/foo_<old_version>_<arch>.deb

This example works even if the dpkg command on the hard disk is broken.

Tip

Any GNU/Linux system started by another system on hard disk, live GNU/Linux CD, bootable USB-key drive, or netboot can be used similarly to rescue broken system.

If attempting to install a package this way fails due to some dependency violations and you really need to do this as the last resort, you can override dependency using dpkg's "--ignore-depends", "--force-depends" and other options. If you do this, you need to make serious effort to restore proper dependency later. See dpkg(8) for details.

Note

If your system is seriously broken, you should make a full backup of system to a safe place (see Section 10.2, “Backup and recovery”) and should perform a clean installation. This is less time consuming and produces better results in the end.

2.6.5. Recovering package selection data

If "/var/lib/dpkg/status" becomes corrupt for any reason, the Debian system loses package selection data and suffers severely. Look for the old "/var/lib/dpkg/status" file at "/var/lib/dpkg/status-old" or "/var/backups/dpkg.status.*".

Keeping "/var/backups/" in a separate partition may be a good idea since this directory contains lots of important system data.

For serious breakage, I recommend to make fresh re-install after making backup of the system. Even if everything in "/var/" is gone, you can still recover some information from directories in "/usr/share/doc/" to guide your new installation.

Then you are presented with package names to install. (There may be some non-package names such as "texmf".)

2.7. Tips for the package management

2.7.1. How to pick Debian packages

You can seek packages which satisfy your needs with aptitude from the package description or from the list under "Tasks".

When you encounter more than 2 similar packages and wonder which one to install without "trial and error" efforts, you should use some common sense. I consider following points are good indications of preferred packages.

Essential: yes > no

Area: main > contrib > non-free

Priority: required > important > standard > optional > extra

Tasks: packages listed in tasks such as "Desktop environment"

Packages selected by the dependency package (e.g., python2.4 by python)

Popcon: higher in the vote and install number

Changelog: regular updates by the maintainer

BTS: No RC bugs (no critical, no grave, and no serious bugs)

BTS: responsive maintainer to bug reports

BTS: higher number of the recently fixed bugs

BTS: lower number of remaining non-wishlist bugs

Debian being a volunteer project with distributed development model, its archive contains many packages with different focus and quality. You must make your own decision what to do with them.

2.7.2. Packages from mixed source of archives

Caution

Installing packages from mixed source of archives is not supported by the official Debian distribution except for officially supported particular combinations of archives such as stable with security updates and jessie-updates.

Here is an example of operations to include specific newer upstream version packages found in unstable while tracking testing for single occasion.

Change the "/etc/apt/sources.list" file temporarily to single "unstable" entry.

Run "aptitude update".

Run "aptitude install <package-name>".

Recover the original "/etc/apt/sources.list" file for testing.

Run "aptitude update".

You do not create the "/etc/apt/preferences" file nor need to worry about apt-pinning with this manual approach. But this is very cumbersome.

Caution

When using mixed source of archives, you must ensure compatibility of packages by yourself since the Debian does not guarantee it. If package incompatibility exists, you may break system. You must be able to judge these technical requirements. The use of mixed source of random archives is completely optional operation and its use is not something I encourage you to use.

General rules for installing packages from different archives are the following.

Non-binary packages ("Architecture: all") are safer to install.

documentation packages: no special requirements

interpreter program packages: compatible interpreter must be available

Binary packages (non "Architecture: all") usually face many road blocks and are unsafe to install.

In order to make a package to be safer to install, some commercial non-free binary program packages may be provided with completely statically linked libraries. You should still check ABI compatibility issues etc. for them.

2.7.3. Tweaking candidate version

Without the "/etc/apt/preferences" file, APT system choses the latest available version as the candidate version using the version string. This is the normal state and most recommended usage of APT system. All officially supported combinations of archives do not require the "/etc/apt/preferences" file since some archives which should not be used as the automatic source of upgrades are marked as NotAutomatic and dealt properly.

When you install packages from mixed source of archives (see Section 2.7.2, “Packages from mixed source of archives”) regularly, you can automate these complicated operations by creating the "/etc/apt/preferences" file with proper entries and tweaking the package selection rule for candidate version as described in apt_preferences(5). This is called apt-pinning.

Warning

Use of apt-pinning by a novice user is sure call for major troubles. You must avoid using apt-pinning except when you absolutely need it.

Caution

When using apt-pinning, you must ensure compatibility of packages by yourself since the Debian does not guarantee it. The apt-pinning is completely optional operation and its use is not something I encourage you to use.

The APT system choses the highest Pin-Priority upgrading package from available package sources defined in the "/etc/apt/sources.list" file as the candidate version package. If the Pin-Priority of the package is larger than 1000, this version restriction for upgrading is dropped to enable downgrading (see Section 2.7.10, “Emergency downgrading”).

Pin-Priority value of each package is defined by "Pin-Priority" entries in the "/etc/apt/preferences" file or uses its default value.

The NotAutomatic and ButAutomaticUpgrades archive is set by archive server having its archive level Release file (see Section 2.5.3, “Archive level "Release" files”) containing both "NotAutomatic: yes" and "ButAutomaticUpgrades: yes". The NotAutomatic archive is set by archive server having its archive level Release file containing only "NotAutomatic: yes".

The apt-pinning situation of <package> from multiple archive sources is displayed by "apt-cache policy <package>".

A line started with "Package pin:" lists the package version of pin if association just with <package> is defined, e.g., "Package pin: 0.190".

No line with "Package pin:" exists if no association just with <package> is defined.

The Pin-Priority value associated just with <package> is listed right side of all version strings, e.g., "0.181 700".

"0" is listed right side of all version strings if no association just with <package> is defined, e.g., "0.181 0".

The Pin-Priority values of archives (defined as "Package: *" in the "/etc/apt/preferences" file) are listed left side of all archive paths, e.g., "100 http://ftp.XX.debian.org/debian/ jessie-backports/main Packages".

There is no need to set Pin-Priority value explicitly in the "/etc/apt/preferences" file. When newer packages become available, the default configuration provides most reasonable upgrades (see Section 2.5.3, “Archive level "Release" files”).

All installed older packages are upgraded to newer ones from jessie-updates.

Only manually installed older packages from jessie-backports are upgraded to newer ones from jessie-backports.

Whenever you wish to install a package named "<package-name>" with its dependency from jessie-backports archive manually, you use following command while switching target release with "-t" option.

$ sudo apt-get install -t jessie-backports <package-name>

2.7.5. Blocking packages installed by "Recommends"

If you wish not to pull in particular packages automatically by "Recommends", you must create the "/etc/apt/preferences" file and explicitly list all those packages at the top of it as the following.

2.7.6. Tracking testing with some packages from unstable

Here is an example of apt-pinning technique to include specific newer upstream version packages found in unstable regularly upgraded while tracking testing. You list all required archives in the "/etc/apt/sources.list" file as the following.

When you wish to install a package named "<package-name>" with its dependencies from unstable archive under this configuration, you issue the following command which switches target release with "-t" option (Pin-Priority of unstable becomes 990).

$ sudo apt-get install -t unstable <package-name>

With this configuration, usual execution of "apt-get upgrade" and "apt-get dist-upgrade" (or "aptitude safe-upgrade" and "aptitude full-upgrade") upgrades packages which were installed from testing archive using current testing archive and packages which were installed from unstable archive using current unstable archive.

Caution

Be careful not to remove "testing" entry from the "/etc/apt/sources.list" file. Without "testing" entry in it, APT system upgrades packages using newer unstable archive.

Tip

I usually edit the "/etc/apt/sources.list" file to comment out "unstable" archive entry right after above operation. This avoids slow update process of having too many entries in the "/etc/apt/sources.list" file although this prevents upgrading packages which were installed from unstable archive using current unstable archive.

Tip

If "Pin-Priority: 1" is used instead of "Pin-Priority: 100" in the "/etc/apt/preferences" file, already installed packages having Pin-Priority value of 100 are not upgraded by unstable archive even if "testing" entry in the "/etc/apt/sources.list" file is removed.

If you wish to track particular packages in unstable automatically without initial "-t unstable" installation, you must create the "/etc/apt/preferences" file and explicitly list all those packages at the top of it as the following.

These set Pin-Priority value for each specific package. For example, in order to track the latest unstable version of this "Debian Reference" in English, you should have following entries in the "/etc/apt/preferences" file.

This apt-pinning technique is valid even when you are tracking stable archive. Documentation packages have been always safe to install from unstable archive in my experience, so far.

2.7.7. Tracking unstable with some packages from experimental

Here is another example of apt-pinning technique to include specific newer upstream version packages found in experimental while tracking unstable. You list all required archives in the "/etc/apt/sources.list" file as the following.

The default Pin-Priority value for experimental archive is always 1 (<<100) since it is NotAutomatic archive (see Section 2.5.3, “Archive level "Release" files”). There is no need to set Pin-Priority value explicitly in the "/etc/apt/preferences" file just to use experimental archive unless you wish to track particular packages in it automatically for next upgrading.

2.7.8. Automatic download and upgrade of packages

The apt package comes with its own cron script "/etc/cron.daily/apt" to support the automatic download of packages. This script can be enhanced to perform the automatic upgrade of packages by installing the unattended-upgrades package. These can be customized by parameters in "/etc/apt/apt.conf.d/02backup" and "/etc/apt/apt.conf.d/50unattended-upgrades" as described in "/usr/share/doc/unattended-upgrades/README".

The unattended-upgrades package is mainly intended for the security upgrade for the stable system. If the risk of breaking an existing stable system by the automatic upgrade is smaller than that of the system broken by the intruder using its security hole which has been closed by the security update, you should consider using this automatic upgrade with configuration parameters as the following.

If you are running an unstable system, you do not want to use the automatic upgrade since it certainly breaks system some day. Even for such unstable case, you may still want to download packages in advance to save time for the interactive upgrade with configuration parameters as the following.

2.7.9. Limiting download bandwidth for APT

If you want to limit the download bandwidth for APT to e.g. 800Kib/sec (=100kiB/sec), you should configure APT with its configuration parameter as the following.

APT::Acquire::http::Dl-Limit "800";

2.7.10. Emergency downgrading

Caution

Downgrading is not officially supported by the Debian by design. It should be done only as a part of emergency recovery process. Despite of this situation, it is known to work well in many incidents. For critical systems, you should backup all important data on the system after the recovery operation and re-install the new system from the scratch.

Search lines in the "/etc/apt/sources.list" file tracking unstable as the following.

deb http://ftp.us.debian.org/debian/ sid main contrib non-free

Replace it with the following to track testing.

deb http://ftp.us.debian.org/debian/ stretch main contrib non-free

Set the "/etc/apt/preferences" file as the following.

Package: *
Pin: release a=testing
Pin-Priority: 1010

Run "apt-get update; apt-get dist-upgrade" to force downgrading of packages across the system.

Remove this special "/etc/apt/preferences" file after this emergency downgrading.

Tip

It is a good idea to remove (not purge!) as much packages to minimize dependency problems. You may need to manually remove and install some packages to get system downgraded. Linux kernel, bootloader, udev, PAM, APT, and networking related packages and their configuration files require special attention.

2.7.11. Who uploaded the package?

Although the maintainer name listed in "/var/lib/dpkg/available" and "/usr/share/doc/package_name/changelog" provide some information on "who is behind the packaging activity", the actual uploader of the package is somewhat obscure. who-uploads(1) in the devscripts package identifies the actual uploader of Debian source packages.

2.7.12. The equivs package

If you are to compile a program from source to replace the Debian package, it is best to make it into a real local debianized package (*.deb) and use private archive.

If you chose to compile a program from source and to install them under "/usr/local" instead, you may need to use equivs as a last resort to satisfy the missing package dependency.

Package: equivs
Priority: extra
Section: admin
Description: Circumventing Debian package dependencies
This is a dummy package which can be used to create Debian
packages, which only contain dependency information.

2.7.13. Porting a package to the stable system

For partial upgrades of the stable system, rebuilding a package within its environment using the source package is desirable. This avoids massive package upgrades due to their dependencies.

Add the following entries to the "/etc/apt/sources.list" of a stable system.

Update some tool chain packages such as dpkg, and debhelper from the
backport packages if they are required for the backporting.

Execute the following.

$ dch -i

Bump package version, e.g. one appended with "+bp1" in "debian/changelog"

Build packages and install them to the system as the following.

$ debuild
$ cd ..
# debi foo*.changes

2.7.14. Proxy server for APT

Since mirroring whole subsection of Debian archive wastes disk space and network bandwidth, deployment of a local proxy server for APT is desirable consideration when you administer many systems on LAN. APT can be configure to use generic web (http) proxy servers such as squid (see Section 6.10, “Other network application servers”) as described in apt.conf(5) and in "/usr/share/doc/apt/examples/configure-index.gz". The "$http_proxy" environment variable can be used to override proxy server setting in the "/etc/apt/apt.conf" file.

There are proxy tools specially for Debian archive. You should check BTS before using them.

When Debian reorganizes its archive structure, these specialized proxy tools tend to require code rewrites by the package maintainer and may not be functional for a while. On the other hand, generic web (http) proxy servers are more robust and easier to cope with such changes.

If you are thinking about managing many servers in a cluster with practically the same configuration, you should consider to use specialized package such as fai to manage the whole system.

2.7.17. Converting or installing an alien binary package

alien(1) enables the conversion of binary packages provided in Red Hat rpm, Stampede slp, Slackware tgz, and Solaris pkg file formats into a Debian deb package. If you want to use a package from another Linux distribution than the one you have installed on your system, you can use alien to convert it from your preferred package format and install it. alien also supports LSB packages.

Warning

alien(1) should not be used to replace essential system packages, such as sysvinit, libc6, libpam-modules, etc. Practically, alien(1) should only be used for non-free binary-only packages which are LSB compliant or statically linked. For free softwares, you should use their source packages to make real Debian packages.

2.7.18. Extracting package without dpkg

The "dpkg*.deb" package contents can be extracted without using dpkg(1) on any Unix-like environment using standard ar(1) and tar(1).

The other "*.deb" package contents can be extracted by the dpkg-deb(1) command obtained from the "dpkg*.deb" package as above; or using standard ar(1) and newer GNU tar(1) with the xz(1) decompression support similarly as above.

You can also browse package content using the mc command.

2.7.19. More readings for the package management

You can learn more on the package management from following documentations.